<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>Document</title>
	<style>
		.f{width: 100px;height: 20px;border: 1px solid #999; position: relative;}
		.f:after{content: "";width: 0;height: 0;border: 10px solid transparent;border-left-color:#999;position:absolute; right: 0;}
	</style>
</head>
<body>
	<div class="f"></div>
</body>
</html>